Abstract:

For a considerable period of time, the issue of agricultural ecological environment security resulting from cadmium pollution in farmland soil has garnered significant attention. However, in comparison to acidic soil, the matter of cadmium contamination in alkaline soil, which is extensively distributed throughout China, has not received adequate recognition. Consequently, addressing the urgent problem of excessive cadmium levels in wheat grains within major grain-producing regions in northern China becomes imperative. In order to investigate the migration and transformation patterns of the heavy metal cadmium within an alkaline soil-crop system, this study utilized typical alkaline cadmium-polluted farmland soil and winter wheat from Jiyuan City, Henan Province as representative examples. By analyzing variations in cadmium content at different growth stages of wheat and examining its distribution across various organs within wheat plants, we were able to elucidate the accumulation, migration, and transformation dynamics of cadmium at the interface between soil and crops during wheat's growth and development stages. Furthermore, this research also shed light on how rhizosphere effects and physicochemical properties of soils influence these processes. The results showed as follows: 1) The changes in physical and chemical properties of rhizosphere soil were more pronounced than those in non-rhizosphere soil during the growth and development of wheat, with a significant accumulation trend of organic matter in the rhizosphere environment (P<0.01). 2) The available cadmium content in soil significantly increased during the wheat filling stage, and was positively influenced by soil organic matter (SOM) in bulk soil (r_BS=0.471, P_BS<0.05; r_RS=0.544, P_RS<0.01), while being negatively inhibited by CEC in the rhizosphere (r_BS= −0.707, P_BS<0.01; r_RS=−0.637, P_RS<0.01). 3) The enrichment capacity of Cd in roots of wheat (R_BCF: range: 0.559‒1.61) was significantly higher than that in stems and leaves (L_BCF range: 0.146‒0.584). Enrichment of Cd in roots mainly occurred at the tillering stage (tillering stage 1.61>filling stage 0.600>mature stage 0.559), while Cd translocation to the aboveground parts concentrated during the filling stage (filling stage 1.04>tillering stage 0.277>mature stage 0.260). 4) The enrichment capacity of cadmium in wheat roots was enhanced with the increased pH of rhizosphere soil (r=0.690, P<0.05), while the enrichment capacity of cadmium in stems and leaves decreased as rhizosphere soil CEC increased (r= −0.697, P<0.05). Therefore, managing key factors such as SOM and CEC during critical periods of cadmium accumulation and migration to wheat (tillering stage, filling stage) can effectively mitigate the risk of cadmium exceeding in wheat grain. The research results provide a theoretical basis for remediating and controlling the risk of alkaline cadmium contaminated farmland soils.

Key words: alkaline farmland soil, cadmium pollution, winter wheat, soil physicochemical properties, bioconcentration and translocation characteristics

摘要：

目前，农田土壤镉污染导致的农业生态环境安全问题引起了极大的关注，然而与酸性土壤相比，针对碱性土壤镉污染导致小麦籽粒镉超标的相关研究进展缓慢。为探明镉在碱性土壤-作物系统中的迁移转化规律，以河南省济源市碱性镉污染农田土壤及冬小麦为例，通过分析小麦不同生育期土壤和小麦植株各器官镉含量的分布变化，阐明了土壤镉随小麦生长发育的富集及迁移转化规律，揭示了根际效应和土壤理化性质对该过程的影响。结果显示：1）随着小麦生长发育，相较于非根际，根际土壤理化性质的变化更为明显，有机质向根际环境的富集趋势显著（P<0.01）;2）土壤镉有效态含量在小麦灌浆期明显上升，且在非根际土壤中受有机质正向促进（r_BS=0.471，P_BS<0.05;r_RS=0.544，P_RS<0.01），而在根际中被CEC负向抑制（r_BS= −0.707，P_BS<0.01;r_RS= −0.637，P_RS<0.01）;3）小麦根部对镉的富集能力（R_BCF：0.559－1.61）显著高于茎叶（L_BCF：0.146－0.584），土壤镉向根部富集主要表现在分蘖期（分蘖期1.61>灌浆期0.600>成熟期0.559），向地上部分迁移转运则集中在灌浆期（灌浆期1.04>分蘖期0.277>成熟期0.260）;4）小麦根部对镉的富集能力随根际土壤pH的升高而增强（r=0.690，P<0.05），茎叶对镉的富集能力随根际土壤CEC的升高而降低（r= −0.697，P<0.05）。由此，在碱性土壤镉污染修复治理中，针对性地在镉向小麦富集迁移的关键期（分蘖期、灌浆期）采取阻控措施，调节关键影响因素（土壤有机质、CEC），可控制小麦籽粒镉超标风险。研究结果可为碱性镉污染农田土壤的修复治理及风险防控提供理论基础。

关键词: 碱性农田土壤, 镉污染, 冬小麦, 土壤理化性质, 富集迁移特性